It is known from prior art, for example from DE 10 2010 045, that a plurality of battery cells can be provided interconnected so as to supply a specified voltage or a specified current to a battery. Such batteries are nowadays used in particular as traction batteries in motor vehicles such as electric vehicles or hybrid vehicle to provide electric drive energy.
With such battery cells, a so-called current interrupt device (CID) can be provided. Such a current interrupt device is provided to trigger an interruption with an excessive current flow, which is to say with an outer short-circuit and additionally or alternative with an increased internal pressure in the battery cell housing. As a result, flowing of the current through the battery cell is prevented, so that there will be no further warming of the battery cell. In this manner, other chemical reactions can be fueled or amplified and a so-called “thermal runaway” of the battery cell is avoided. At the same time, however, the function of the battery cell the discharging or receiving of the electric current, is no longer provided.
In the case of commercially available battery cells, such as those that are used for traction batteries of motor vehicles, a current interrupting device can be provided such as the one illustrated in the reference of FIG. 1 In a schematically illustrated battery cell 10 is in this case partially indicated a battery cell housing 12, in which is arranged a galvanic element 14. Between an arrester 16 of the galvanic element 14 and an electric connection 18 of the battery cell 10 is arranged the current interrupting device 20 which in the case of the battery cell 10 comprises a metal sheet 22 which can be deformed as a result of external influences. The metal sheet 22 accordingly functions as a bimetal element whose deformation depends on the temperature. In the initial state, the metal sheet 22 is also connected at the arrester 16 as shown in FIG. 1. However, with an increased temperature or with an increased pressure, the metal sheet 22 becomes arched within the battery cell housing 12, for example as a result of the development of gas.
This is further illustrated in FIG. 2. As a result, an electrically conductive connection between the arrester 16 and the electric connection 18 in interrupted. The arrester 16 is a part of an electrode of the galvanic element 14, which in addition to the arrester 16 comprises also a chemically active material (not shown in the figure) of the electrode.
Furthermore, EP 2 306 485 A1 describes a battery cell with a current interrupting device which is formed as a fuse. With the melting of for instance a zinc material, the contact between an arrester of a galvanic element and an electric connection or a pole of the battery cell is permanently interrupted.
The fact such current interrupting devices must be viewed as comparatively expensive components is to be regarded as a disadvantage of these battery cells. In addition, a number of compromises must be addressed in the design of such current interrupters. The triggering function is in particular comparable to the function of an electric fuse. Accordingly, the pressure, the temperature and the intensity of the current, as well as the time period over which such large variables are present play an important role with respect to the triggering conduct. As a result, corresponding characteristic curves of these parameters overlap and hysteresis can occur. The result is that an exact triggering threshold value can be predetermined only with difficulty. It is indeed difficult to take into account as much as possible also the interaction of the different factors. Moreover, trying to make a suitable adjustment for each battery cell type with respect to these factors is very laborious as well.
In addition, such a mechanical current interrupting device can be triggered only once. In other words, the current interrupting device cannot be reset after it has been triggered and the current interruption is therefore irreversible. Moreover, such a mechanical component requires a great precision for the manufacturing of the battery cell so that the current interrupting device could perform its desired function.
With a battery cell provided with a current interrupting device which causes triggering also in the case when the internal pressure rises in the battery cell housing, so-called overcharging additives are as a rule also used. Such additives lead with overcharging of the battery cells to releasing of gases and to an increase of internal pressure. Moreover, the introduction of such overcharging additives is not desirable because an increase of the internal pressure in the battery cell housing should be prevented as much as possible. Overcharging additives in addition also lead to a slow, constant increasing of the pressure in the interior of the battery cell housing. As a result, during the course of time and in particular at a point in time that cannot be predicted, an undesirable triggering of the current interrupting device occurs.
That is why there are also battery cells without a current interrupting device which do not contain gaseous additives intended to prevent the pressure in the cells from being unnecessarily increased. That is why current interrupting devices and their advantages and disadvantages are passionately and controversially discussed. The problem is that on the one hand, the current interrupting device of the battery cell should be as reliable and as robust on possible. On the other hand, the current interrupting device should be also as sensitive with respect to triggering as possible.